Mechanoluminescent elastic composite material and preparation method thereof

Abstract

The invention relates to mechanoluminescent elastic composites and methods of making the same. The preparation method of the mechanoluminescent elastic composite material comprises the following steps: mixing raw materials of the mechanoluminescent elastic composite material, and then performing first curing to obtain the mechanoluminescent elastic composite material; the mechanoluminescence elastic composite material is prepared from the following raw materials: a flexible matrix precursor and luminescent particles, wherein the flexible matrix precursor is cured to form a flexible matrix of the mechanoluminescence elastic composite material; the tensile elastic modulus of the composite material test sample is A, the tensile elastic modulus of the flexible matrix test sample is B, and A and B meet the condition that (A-B) / B is larger than or equal to 25%; the difference value between the Zeta potential of the flexible matrix test sample and the Zeta potential of the light-emitting particles is greater than or equal to 10mV. According to the mechanoluminescence elastic composite material prepared through the method, the surface of the flexible substrate and the surfaces of the light-emitting particles have high interface acting force, and the light-emitting intensity of the mechanoluminescence elastic composite material is improved.

Description

Technical Field

[0001] This invention relates to the field of luminescent materials technology, and in particular to mechanoluminescent elastic composite materials and their preparation methods. Background Technology

[0002] Mechanoluminescence (ML) refers to the phenomenon of light radiation produced when a material undergoes mechanical energy input processes such as contact, friction, deformation, or fracture. It is sometimes also called mechanical luminescence. Excitation forms of mechanoluminescence include, but are not limited to, mechanical actions such as material fracture, friction, tensile and compressive deformation, and contact separation. This characteristic of directly converting force into light without the need for other media has a natural advantage in converting mechanical energy into light energy, allowing people to fully utilize the mechanical energy widely available in daily production and life. In recent years, with the rapid development of energy harvesting and utilization, flexible electronics, and intelligent sensing, mechanoluminescence, as an important pathway for energy conversion and dissipation, has significant scientific implications for controlling energy dissipation and has enormous application value in the interdisciplinary fields of functional materials and devices.

[0003] Currently, materials with high mechanoluminescence intensity are generally inorganic crystalline materials, such as ZnS doped with transition metal elements and strontium aluminate doped with lanthanides. Many materials with mechanoluminescence properties also possess electroluminescence properties. When faced with a variety of external stimuli, such as tensile and compressive deformation, friction, and contact separation, a single mechanoluminescent material, due to its own mechanical properties and luminescence limitations, can often only provide limited responses and feedback to some of these situations.

[0004] In the research and application of mechanoluminescence, researchers often combine mechanoluminescent materials with flexible transparent materials to improve the mechanoluminescence conversion efficiency and adaptability to complex environments. However, the drawback of existing mechanoluminescent composite elastomers is that the mechanoluminescence brightness is relatively low. Summary of the Invention

[0005] Therefore, it is necessary to provide a mechanoluminescent elastic composite material that can improve the intensity of mechanoluminescence and its preparation method.

[0006] One aspect of the present invention provides a method for preparing a mechanoluminescent elastic composite material, comprising the following steps:

[0007] The raw materials of the mechanoluminescent elastic composite material are mixed and then subjected to a first curing process to obtain the mechanoluminescent elastic composite material.

[0008] The raw materials of the mechanoluminescent elastic composite material include a flexible matrix precursor and luminescent particles. The flexible matrix precursor is cured to form the flexible matrix of the mechanoluminescent elastic composite material.

[0009] The flexible matrix precursor and the luminescent particles are mixed evenly according to the ratio of the flexible matrix precursor and the luminescent particles in the raw material and poured into the cavity of the hollow mold. After degassing for 10 minutes under a vacuum of -0.09MPa, a second curing is carried out to form a composite material test sample. The tensile elastic modulus of the composite material test sample is A.

[0010] The flexible matrix precursor is cast into the cavity of a hollow mold, degassed for 10 minutes under a vacuum of -0.09 MPa, and then subjected to a third curing process to form a flexible matrix test sample. The tensile elastic modulus of the flexible matrix test sample is B.

[0011] The conditions for the second and third curing processes are exactly the same as those for the first curing process;

[0012] A and B satisfy: (AB) / B≥25%;

[0013] The difference between the Zeta potential of the flexible substrate test sample and the Zeta potential of the luminescent particles is ≥10mV.

[0014] In some embodiments, the method for preparing the mechanoluminescent elastic composite material satisfies at least one of the following characteristics:

[0015] The raw materials of the mechanoluminescent elastic composite material meet the following requirements: 25% ≤ (AB) / B ≤ 100%;

[0016] The raw materials of the mechanoluminescent elastic composite material satisfy the following condition: the difference between the Zeta potential of the flexible matrix test sample and the Zeta potential of the luminescent particles is ≥15mV.

[0017] In some embodiments, the method for preparing the mechanoluminescent elastic composite material satisfies at least one of the following characteristics:

[0018] The material of the luminescent particles includes any one or more of zinc sulfide doped with copper, zinc sulfide doped with manganese, strontium sulfide doped with copper, and strontium sulfide doped with cerium.

[0019] The luminescent particles have an aluminum oxide coating layer with a thickness of 10 nm to 2 μm.

[0020] The D50 particle size of the luminescent particles is 20 μm-30 μm. In some embodiments, the method for preparing the mechanoluminescent elastic composite material satisfies at least one of the following characteristics:

[0021] The flexible matrix precursor includes any one or more of polyurethane prepolymer, modified polydimethylsiloxane prepolymer, and modified polyethylene terephthalate prepolymer.

[0022] The visible light transmittance of the flexible substrate is ≥85%.

[0023] In some embodiments, the mass percentage of the luminescent particles in the raw materials of the mechanoluminescent elastic composite material is 20% to 40%.

[0024] In some embodiments, the luminescent particles are zinc sulfide-doped copper coated with alumina.

[0025] In some embodiments, the flexible matrix precursor is a polyurethane prepolymer.

[0026] In some embodiments, the polyurethane prepolymer includes at least one of the following characteristics:

[0027] The polymer monomers of the polyurethane prepolymer include polytetrahydrofuran and toluene-2,4-diisocyanate. Optionally, the molar ratio of polytetrahydrofuran to toluene-2,4-diisocyanate is 1:2 to 1:2.2.

[0028] The chain extender of the polyurethane prepolymer is any one or more of N-methyldiethanolamine, diethanolamine, triethanolamine, 1,4-butanediol, and methylpropanediol;

[0029] The number-average molecular weight of the polyurethane prepolymer is 40,000 g / mol to 70,000 g / mol.

[0030] In some embodiments, the step of mixing the raw materials of the mechanoluminescent elastic composite material and then performing a first curing includes:

[0031] The raw material of the mechanoluminescent elastic composite material is introduced into a mold for first curing, and the cured material is separated from the mold; the mold is a hollow mold or a mold with pores; optionally, the mold with pores can be dissolved in a solution to achieve separation from the cured material.

[0032] The second aspect of this application provides a mechanoluminescent elastic composite material, comprising a flexible matrix and luminescent particles distributed in the flexible matrix, and prepared by any of the above-described methods for preparing mechanoluminescent elastic composite materials.

[0033] This application selects a flexible matrix precursor and luminescent particles that satisfy the above-mentioned elastic modulus relationship. On the one hand, the surface of the flexible matrix formed after the flexible matrix precursor is cured and molded has a strong interfacial force with the surface of the luminescent particles, which can increase the bonding force between the luminescent particles and the flexible matrix, improve the efficiency of transmitting external forces to the luminescent particles through the flexible matrix, and increase the stress on the luminescent particles under the same deformation conditions. Then, the mechanical-optical energy conversion is achieved by the mechanoluminescence properties of the luminescent particles themselves. On the other hand, the surface of the flexible matrix formed after the flexible matrix precursor is cured and molded has a large difference in electronegativity with the surface of the luminescent particles, which can enhance the charge transfer when the luminescent particles and the flexible matrix are separated at contact, increase the particle wall separation electric field intensity generated by contact separation, increase the electric field on the luminescent particles under the same deformation conditions, and then the mechanical-electric-optical energy conversion is achieved by the electroluminescence properties of the luminescent particles themselves. Thus, the luminescence intensity of the mechanoluminescent elastic composite material is comprehensively improved. Attached Figure Description

[0034] Figure 1 The graph shows a comparison of the mechanical properties of the flexible matrix composite luminescent particles in Example 1 and Comparative Example 1.

[0035] Figure 2 Scanning electron microscope images of the bonding state between the flexible substrate and the luminescent particles in Example 1 and Comparative Example 1.

[0036] Figure 3 The infrared absorption spectra of the flexible matrix and luminescent particles before and after being combined in Example 1 and Comparative Example 1 are shown.

[0037] Figure 4 This is a schematic diagram of the zeta potential of the flexible substrate and the surface of the luminescent particles in Example 1 and Comparative Example 1.

[0038] Figure 5 This is a comparison diagram of the macroscopic luminescence effects of the mechanoluminescent elastic composite materials of Example 1 and Comparative Example 1;

[0039] Figure 6 The diagram shows the luminescence measurement device and luminescence effect test diagram of the mechanoluminescent elastic composite material of Example 1 and Comparative Example 1.

[0040] Figure 7 Here are schematic diagrams and scanning electron microscope images of the porous mechanoluminescent elastic composite material of Example 2;

[0041] Figure 8 This is a three-dimensional perspective view of the internal structure of the porous mechanoluminescent elastic composite material of Example 2;

[0042] Figure 9 Comparison of the macroscopic luminescence effects of the mechanoluminescent elastic composite materials in Examples 1 and 2;

[0043] Figure 10 The diagram shows the measuring device, luminescence test results, and elastic strain curves of the mechanoluminescent elastic composite materials in Examples 1 and 2. Detailed Implementation

[0044] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0046] Currently, existing mechanoluminescent composite elastomers suffer from low mechanoluminescence intensity. To address this issue, this application provides at least one mechanoluminescent elastic composite material and its preparation method.

[0047] According to a typical embodiment of this application, a method for preparing a mechanoluminescent elastic composite material is provided, comprising the following steps: mixing raw materials for the mechanoluminescent elastic composite material and then subjecting them to a first curing process to obtain the mechanoluminescent elastic composite material; the raw materials for the mechanoluminescent elastic composite material include a flexible matrix precursor and luminescent particles, and the flexible matrix precursor is cured to form the flexible matrix of the mechanoluminescent elastic composite material.

[0048] The flexible matrix precursor and luminescent particles are mixed evenly according to the ratio of the flexible matrix precursor and luminescent particles in the raw material and poured into the cavity of the hollow mold. After degassing for 10 minutes under a vacuum of -0.09MPa, a second curing is carried out to form a composite material test sample. The tensile elastic modulus of the composite material test sample is A.

[0049] The flexible matrix precursor was cast into the cavity of the hollow mold, degassed for 10 minutes under a vacuum of -0.09MPa, and then subjected to a third curing process to form a flexible matrix test sample. The tensile elastic modulus of the flexible matrix test sample is B.

[0050] The conditions for the second and third curing processes are exactly the same as those for the first curing process;

[0051] A and B satisfy: (AB) / B≥25%;

[0052] The difference between the Zeta potential of the flexible substrate test sample and the Zeta potential of the luminescent particles is ≥10mV.

[0053] This application selects a flexible matrix precursor and luminescent particles that satisfy the above-mentioned elastic modulus relationship. After the flexible matrix precursor is cured and molded, the surface of the flexible matrix and the surface of the luminescent particles have a strong interfacial force, which can increase the bonding force between the luminescent particles and the flexible matrix, improve the efficiency of transmitting external forces to the luminescent particles through the flexible matrix, increase the stress on the luminescent particles under the same deformation conditions, and then realize the mechanical-light energy conversion through the mechanoluminescence properties of the luminescent particles themselves, thereby improving the luminescence intensity of the mechanoluminescent elastic composite material.

[0054] The luminescence mechanism of mechanoluminescent composite elastomers generally consists of two parts: (1) stress-induced luminescence: the flexible matrix material can transfer stress to the luminescent particles to induce luminescence; (2) particle wall separation electric field-induced luminescence: the particle wall separation is generated by the deformation difference between the hard luminescent particles and the flexible matrix, forming a contact separation electric field that induces electroluminescence in the particles. Considering the particle wall separation electric field-induced luminescence mechanism of mechanoluminescent composite elastomers, in order to further improve the luminescence intensity of mechanoluminescent composite materials, when preparing mechanoluminescent elastic composite materials, a flexible matrix precursor and luminescent particles are selected. The difference between the Zeta potential of the flexible matrix test sample and the Zeta potential of the luminescent particles is ≥10mV. The Zeta potential is a measure of the ability of the surface to attract charges in the solution. The Zeta potential difference between the flexible matrix material and the luminescent particles reflects the electronegativity difference between the flexible matrix material and the luminescent particles. A large Zeta potential difference makes the electronegativity difference between the flexible matrix material and the surface material of the luminescent particles large, which can promote significant charge transfer during the contact separation process, enhance the contact separation electric field, and thus promote the improvement of the luminescence intensity of the mechanoluminescent elastic composite material.

[0055] For example, the test method for tensile modulus of elasticity can be carried out in accordance with the relevant provisions of GB / T 2567-2021. In the preparation process, the mold specifications adopt the dumbbell shape used in the standard tensile strength test (effective width 10 mm, effective length 50 mm, thickness 4 mm).

[0056] Understandably, the hollow mold used to prepare composite material test samples and flexible matrix test samples contains no structure within the cavity that would allow the test sample to form a hole, such as a dumbbell-shaped cavity; that is, the composite material test sample and flexible matrix test sample are dense structures. In some embodiments, the prepared composite material test sample and flexible matrix test sample are dumbbell-shaped, with a total length of 210±10 mm, a total width of 20±0.5 mm, and a total thickness of 4±0.2 mm. The effective length is 50±0.5 mm, the effective width is 10±0.2 mm, and the effective thickness is 4±0.2 mm. The standard specimen shape and dimensions can be found in GB / T 2567-2021. Figure 1 "Tension Specimen" and "Table 1 Tension Specimen Dimensions".

[0057] Non-limiting, the value of (AB) / B can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc. Optionally, the raw materials of the mechanoluminescent elastic composite material satisfy: 25% ≤ (AB) / B ≤ 100%.

[0058] Non-limitingly, when selecting the flexible matrix precursor and luminescent particles, the difference between the Zeta potential of the flexible matrix test sample and the Zeta potential of the luminescent particles can be 10 mV, 12 mV, 15 mV, 18 mV, 20 mV, 22 mV, 25 mV, 28 mV, 30 mV, 33 mV, 35 mV, 38 mV, 40 mV, etc. In some embodiments, the raw materials of the mechanoluminescent elastic composite material satisfy the following: the difference between the Zeta potential of the flexible matrix test sample and the Zeta potential of the luminescent particles is ≥15 mV.

[0059] For example, a solid surface zeta potential meter (such as SurPASS, Anton Parr) can be used to measure the zeta potential of a flexible substrate test sample or luminescent particles using a 0.1 mM KCl solution (with a conductivity of 1.3 μS / cm) as a low-concentration dielectric.

[0060] Strong interfacial interactions between the flexible matrix material and the surface of the luminescent particles are generally achieved through secondary bonding interactions such as van der Waals forces and hydrogen bonds between surface molecules. Electronegativity difference refers to the relative magnitude of the charge transfer capabilities of the materials. Specifically, these two aspects can be addressed by directly selecting a suitable flexible polymer as the matrix material based on the crystal structure, molecular groups, and other material properties of the luminescent particle surface; or by selectively modifying the molecular chain groups of existing flexible polymer materials; or by selectively coating or grafting special molecular groups onto the surface of existing luminescent particles; or by simultaneously adapting and modifying both existing luminescent particles and flexible matrix materials to create strong interfacial interactions and significant electronegativity differences between their surfaces.

[0061] In some embodiments, the material of the luminescent particles includes any one or more of zinc sulfide-doped copper, zinc sulfide-doped manganese, strontium sulfide-doped copper, and strontium sulfide-doped cerium, which is beneficial to improving the luminescence intensity of the mechanoluminescent elastic composite material.

[0062] In some embodiments, the luminescent particles have an alumina coating layer. This coating layer can prevent water and oxygen permeation and ZnS reaction deliquescence, and improve the surface hardness and modulus of the particles. Furthermore, the luminescent particles with the alumina coating layer have a lower zeta potential, making it easier to form a larger electronegativity difference with the flexible matrix, thereby enhancing the luminescence intensity of the mechanoluminescent elastic composite material. Optionally, the thickness of the alumina coating layer is 10 nm to 2 μm, which not only provides good coating but also good light transmittance. Non-limitingly, the thickness of the alumina coating layer can be 10 nm, 100 nm, 500 nm, 800 nm, 1 μm, 1.5 μm, 2 μm, etc.

[0063] In some embodiments, the D50 particle size of the luminescent particles is 20 μm-30 μm. Non-limitingly, the D50 particle size of the luminescent particles is 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, etc.

[0064] In some embodiments, the flexible matrix precursor includes any one or more of polyurethane prepolymer, modified polydimethylsiloxane prepolymer, and modified polyethylene terephthalate prepolymer; the modified polydimethylsiloxane prepolymer and the modified polyethylene terephthalate prepolymer can be materials modified by grafting amino, fluorine-containing groups, sulfur groups, etc.

[0065] In some embodiments, the mass percentage of luminescent particles in the raw materials of the mechanoluminescent elastic composite material is 20% to 40%, which results in superior luminescence performance. Non-limitingly, the mass percentage of luminescent particles in the raw materials of the mechanoluminescent elastic composite material can be 20%, 25%, 30%, 35%, 40%, etc.

[0066] In some embodiments, the light transmittance of the flexible matrix is ​​≥85%. It should be noted that selecting a flexible matrix with high light transmittance ensures high transparency of the light generated by the luminescent particles, i.e., high light transmittance in the luminescent wavelength range. This avoids the reflection, scattering, and absorption of the luminescence by the flexible matrix itself, thereby reducing the impact on the overall luminescence intensity of the composite elastomer.

[0067] In some embodiments, the luminescent particles are zinc sulfide-doped copper (ZnS:Cu), and further, the flexible matrix precursor is a polyurethane prepolymer. Since there are many types of urethane prepolymers in the prior art, the properties of polyurethane materials formed by curing different urethane prepolymers vary greatly. A suitable PU prepolymer can be selected based on the above-mentioned requirements for elastic modulus and optionally Zeta potential.

[0068] Optionally, the polymer monomers of the polyurethane prepolymer include polytetrahydrofuran and toluene-2,4-diisocyanate. Optionally, the molar ratio of polytetrahydrofuran to toluene-2,4-diisocyanate is 1:2 to 1:2.2. Simultaneously, N-methyldiethanolamine is used as the chain extender in the polyurethane prepolymer, resulting in an appropriate proportion of NH groups in the prepared flexible matrix. This increases the bonding force with PU and improves the stress transfer capability from the flexible matrix to the luminescent particles. Furthermore, it enhances the electronegativity of the polyurethane chain segments, increasing charge transfer between the flexible matrix and the surface of the luminescent particles, thereby improving the luminescence intensity of the elastic composite material. In addition, excessively high toluene-2,4-diisocyanate content in the polymer monomers is detrimental to improving the flexibility and ductility of the polyurethane material. Optionally, the chain extender of the polyurethane prepolymer is any one or more of N-methyldiethanolamine, ethanolamine, triethanolamine, 1,4-butanediol, and methylpropanediol. Optionally, the molar ratio of polytetrahydrofuran to the chain extender is 1:1 to 1:1.2. Optionally, the curing conditions for polyurethane are heating at 50~80℃ for 30~60 minutes.

[0069] Optionally, the number-average molecular weight of the polyurethane prepolymer is 40,000 g / mol to 70,000 g / mol.

[0070] Optionally, before performing the first curing process, the raw materials of the mixed mechanoluminescent elastic composite material are first evacuated to fully degas.

[0071] In some embodiments, the step of mixing the raw materials of the mechanoluminescent elastic composite material and then performing a first curing includes: introducing the raw materials of the mechanoluminescent elastic composite material into a mold for a first curing, and separating the cured material from the mold; the mold is a hollow mold or a mold with pores. In some embodiments, using a mold with pores enhances the compressive deformation capacity of the elastic composite material, which is beneficial for increasing the deformation of the elastic composite material under the same load, thereby increasing the luminescence intensity during the compression deformation process.

[0072] Alternatively, the porous mold can be dissolved in a solvent to achieve separation from the cured material.

[0073] In some embodiments, the above-mentioned mechanoluminescent elastic composite material is prepared using a sacrificial template method. Specifically, the step of mixing the raw materials of the mechanoluminescent elastic composite material and then performing a first curing includes: mixing a flexible matrix precursor with luminescent particles to form a raw material mixture; completely immersing a sacrificial template in the uncured raw material mixture and placing it in a vacuum device for degassing; after the degassing is completed, performing a first curing under suitable environmental conditions according to the type of flexible precursor; and removing the sacrificial template after curing to obtain the above-mentioned mechanoluminescent elastic composite material.

[0074] According to another typical embodiment of this application, a mechanoluminescent elastic composite material is provided, which is prepared by any of the above-described methods for preparing mechanoluminescent elastic composite materials.

[0075] In the mechanoluminescent elastic composite material of this application, the flexible matrix has a relatively low elastic modulus and high deformation capacity, which can uniformly transfer external mechanical stress to the embedded mechanoluminescent particles, avoiding material damage caused by severe external impacts and excessive stress concentration. On the other hand, the high transparency of the flexible matrix itself allows photons generated by mechanoluminescence to efficiently penetrate the coated matrix, reducing light scattering and absorption losses. Moreover, the flexible matrix has high chemical stability, which can protect the mechanoluminescent particles from environmental water and oxygen corrosion, extending the material's lifespan. In addition, the combination of the flexible matrix and luminescent particles greatly improves the processability, structural design flexibility, biocompatibility, and wearability of mechanoluminescence applications. Furthermore, due to the above-mentioned preparation method, the mechanoluminescent elastic composite material of this application has a high luminescence intensity.

[0076] The following are specific examples.

[0077] Example 1

[0078] The preparation process of the mechanoluminescent elastic composite material is as follows:

[0079] (1) Preparation of polyurethane prepolymer (PU)

[0080] ① After drying the polyol PTMG at 120 ℃ for 1 h and removing water, dry nitrogen gas is introduced for protection.

[0081] ② After the polyol PTMG is cooled, it is mixed with the isocyanate TDI in a molar ratio of 1:2, while maintaining a dry nitrogen atmosphere for protection.

[0082] ③ After uniform mixing, magnetically stir in an oil bath at 80 ℃ for 1~2 hours;

[0083] ④ After drying and dehydrating the chain extender MDEA at 80 ℃ for 1 h, dry nitrogen gas is introduced for protection.

[0084] ⑤ Cool the chain extender MDEA and the oil bath prepolymer mixture to room temperature, mix them evenly, and let them stand for 10 minutes to carry out the chain extension reaction to obtain a polyurethane prepolymer. The molar ratio of PTMG, TDI and MDEA is 1:2:1, and the number average molecular weight of the polyurethane prepolymer is 50,000 g / mol.

[0085] The main raw materials used in the preparation of polyurethane prepolymers are shown in Table 1 below.

[0086] Table 1

[0087]

[0088] (2) Raw material mixing and curing

[0089] ① The ZnS:Cu luminescent particles were added to the extended PU at a mass ratio of 1:3. After stirring evenly, the mixture was poured into a mold and then vacuum degassed for 10 minutes. The ZnS:Cu luminescent particles were purchased from Shanghai Keyan Optoelectronic Technology Co., Ltd. as ZnS:Cu@Al2O3 particles (model D512 CT). The particle diameter was approximately 25-30 μm, and they had an Al2O3 coating layer with a thickness of 250 nm to 1000 nm. For ease of writing, this embodiment refers to the luminescent particles as ZnS:Cu particles.

[0090] ② Place the mold in a constant temperature drying oven and cure at 70 ℃ for 40 minutes to obtain ZnS:Cu / PU composite luminescent elastomer.

[0091] Comparative Example 1

[0092] The polydimethylsiloxane (PDMS) matrix used was Sylgard 184 from Dow Corning. The specific steps for combining it with the luminescent particles were as follows:

[0093] ① Mix the PDMS precursor and curing agent evenly at a mass ratio of 10:1 to form a PDMS prepolymer;

[0094] ② Add ZnS:Cu luminescent particles (same as in Example 1) to the PDMS prepolymer and stir until homogeneous, wherein the mass ratio of luminescent particles to PDMS is 1:3;

[0095] ③ Pour the above mixture into a mold and then degas it under vacuum for 10 minutes; ④ Place the mold in a constant temperature drying oven at 70℃ and cure it for 1 hour to obtain the ZnS:Cu / PDMS composite luminescent elastomer.

[0096] To accurately and quantitatively assess the interfacial interaction forces between different matrices and luminescent particles, and in conjunction with subsequent tensile intensity tests, the mechanical property parameters (i.e., tensile modulus of elasticity) of the standard dumbbell-shaped composite elastomer were measured. According to the relevant provisions of GB / T 2567-2021, the mold specifications used in the preparation process adopted the standard dumbbell shape (effective width 10 mm, effective length 50 mm, thickness 4 mm) for tensile strength testing. The test samples based on the PDMS matrix were prepared under the same vacuum and curing conditions as Comparative Example 1, and the test samples based on the PU matrix were prepared under the same vacuum and curing conditions as Example 1. Tensile strength tests were performed using an electronic universal testing machine (ZWICKZ020, Zwick), and the results are as follows: Figure 1 As shown in the figure, (a) is the tensile stress-strain curve of pure PDMS elastomer; (b) is the tensile stress-strain curve of ZnS:Cu / PDMS composite elastomer; (c) is the tensile stress-strain curve of pure PU elastomer; and (d) is the tensile stress-strain curve of ZnS:Cu / PU composite elastomer.

[0097] from Figure 1 As can be seen, compared with pure PDMS and pure PU elastomers, both have relatively low elastic moduli with little difference. However, after being composited with 25% luminescent particles, the tensile elastic modulus of the PDMS matrix increased by approximately 17% due to the filling effect of the hard inorganic particles. Compared with the PDMS matrix, the addition of luminescent particles to the PU matrix increased the tensile elastic modulus of the elastomer to a higher level (1.95 MPa), a significant increase of approximately 33%, which is nearly twice the increase in modulus of the PDMS matrix caused by the luminescent particles. This indicates that, in addition to the simple microparticle filling effect, the addition of luminescent particles to the flexible PU matrix involves other interactions between the luminescent particles and the PU matrix, which enhance the bonding force between the two, thereby significantly increasing the tensile elastic modulus.

[0098] The fracture cross-sectional morphology of the specimens after tensile strength testing was characterized and observed using SEM, such as... Figure 2As shown, (a) is the microstructure of the ZnS:Cu / PDMS composite elastomer prepared in Comparative Example 1, and (b) is the microstructure of the ZnS:Cu / PU composite elastomer prepared in Example 1. The SEM images reveal obvious gaps around the luminescent particles in the PDMS matrix, while the luminescent particles in the PU matrix are more tightly bonded to the surrounding matrix. This is consistent with the tensile strength test results, demonstrating an interfacial interaction between the PU matrix and the luminescent particles. This interaction enhances the bonding force between the particles and the PU matrix molecular chains, which is beneficial for improving stress transfer from the flexible matrix to the luminescent particles.

[0099] To further confirm the interaction between the luminescent particles and the flexible matrix, the infrared absorption spectra of the pure matrix, the composite elastomer, and the luminescent particles themselves were characterized using a Fourier transform infrared spectrometer (Vertex 80V, Bruker). The results are as follows: Figure 3 As shown, (a) is the infrared absorption spectrum before and after the PDMS matrix and luminescent particles are combined; (b) is the infrared absorption spectrum before and after the PU matrix and luminescent particles are combined. The inset is a magnified view of the NH bond absorption peak. For the luminescent particles, due to the shielding effect of the surface Al2O3 film, the particles only show infrared absorption in the 400-800 cm⁻¹ range. -1 The luminescent particles exhibit broadband absorption at the Al-O vibration, with no significant absorption at other positions. Therefore, the luminescent particles, when combined with the flexible matrix, do not significantly affect the infrared absorption spectrum of the matrix. However, it is noteworthy that, compared to the pure PU elastomer sample, the NH bond characteristic peak of the ZnS:Cu / PU composite elastomer shifts slightly to the right. This indicates an interaction between the surface of the luminescent particles and the abundant amino groups present in the PU molecular chain.

[0100] Considering the composite preparation process and the presence of alumina on the particle surface, the interfacial interaction should be NH…O, i.e., interfacial hydrogen bonding, resulting in a strong bond between the luminescent particles and the PU matrix, thus improving the stress transfer capability from the flexible matrix to the luminescent particles. When the composite elastomer deforms due to external excitation, the interfacial interaction between the PU matrix and the luminescent particles enhances the stress on the particles, resulting in a greater luminescence intensity compared to luminescent particles in a PDMS matrix. In terms of macroscopic mechanical properties, this is directly manifested as a significant increase in the tensile elastic modulus, improving the efficiency of transferring external forces to the luminescent particles through the flexible matrix, and increasing the stress on the luminescent particles under the same deformation conditions. Therefore, the composite of the PU matrix and luminescent particles should produce higher mechanoluminescence brightness.

[0101] The zeta potentials of the luminescent particles, the aforementioned pure PDMS elastomer, and the pure PU elastomer surface were measured. A solid surface zeta potential meter (SurPASS, Anton Parr) was used, with 0.1 mM KCl solution (conductivity 1.3 μS / cm) as a low-concentration dielectric. The results are as follows: Figure 4 As shown, the difference in Zeta potential between the PDMS and PU matrices relative to the luminescent particle surfaces indicates that during the contact separation process between the luminescent particles and the flexible matrix, the matrix surface tends to acquire negative charges, becoming negatively potentialed, while the particle surface is more likely to become positively potentialed. Furthermore, the potential difference between the two is much larger in the PU matrix than in the PDMS matrix. Therefore, compared to the PDMS matrix, the interfacial charge transfer during particle wall separation in the PU matrix is ​​more significant, resulting in a stronger contact separation electric field.

[0102] To visually compare the luminescence effects of different flexible matrix composite elastomers, a commercial camera (EOS R6 Mark II, Canon) was used to capture and record the luminescence process of stretched ZnS:Cu / PDMS and ZnS:Cu / PU composite elastomers. The results are as follows: Figure 5 As shown, (a) is the stretching and luminescence effect of ZnS:Cu / PDMS under indoor light; (b) is the stretching and luminescence effect of ZnS:Cu / PDMS in a dark room; (c) is the stretching and luminescence effect of ZnS:Cu / PU under indoor light; and (d) is the stretching and luminescence effect of ZnS:Cu / PU in a dark room. Figure 5 It can be seen that the luminescence of ZnS:Cu / PDMS composite elastomer is difficult to observe under indoor light conditions, and can only be observed in a dark room. In contrast, the bright luminescence of ZnS:Cu / PU is visible to the human eye under indoor light conditions, and the contrast between the two is more obvious in a dark room.

[0103] To accurately and quantitatively evaluate the mechanoluminescence intensity of composite elastomers with different matrices, the standard dumbbell-shaped specifications were used to perform tensile light intensity measurements on the standard dumbbell-shaped composite elastomers. The spectral and light intensity measurement device for the tensile composite elastomers is as follows: Figure 6 As shown in (a), the linear displacement motor reciprocates between the initial position and a displacement of 4 mm (corresponding to a strain of 10%) at a fixed speed of 23.7 mm / s. A spectrometer (HRS-300SS, Princeton) and a single-photon counter (C8855-01, Hamamatsu) measured the tensile emission spectrum of the composite elastomer, the emission intensity during the first stretch, and the emission intensity after 1000 stretch cycles via optical fiber (1 mm inlet diameter). The results are as follows: Figure 6 As shown in (b)-(c).

[0104] Compared to the PDMS matrix, the luminescence intensity of the mechanoluminescent elastomer composite with the PU matrix increased significantly (over 147%), indicating a higher force-to-light conversion efficiency between the PU matrix and the luminescent particles. After 1000 tensile cycles, both showed a slight decrease, with ZnS:Cu / PDMS showing a 6.5% decrease and ZnS:Cu / PU a 3.4% decrease. This may be due to mechanical damage caused by repeated tensile cycles to the composite elastomer. The smaller decrease in intensity of ZnS:Cu / PU demonstrates its higher stability and durability in mechanoluminescence. It is evident that the PU flexible matrix with a significantly larger increase in elastic modulus after compositing with luminescent particles, and the zeta potential significantly different from that of the luminescent particles, combined with ZnS:Cu, exhibits higher luminescence intensity and more stable luminescence performance. Furthermore, the emission spectra of both are essentially the same, indicating that their luminescence sources are consistent, consisting of stress excitation and contact separation electric field excitation.

[0105] Example 2

[0106] The difference from Example 1 is that in step ① of the raw material mixing and solidification process, a different mold is used; instead, a water-soluble sugar cube (19×12×20 mm) with micropores is employed. 3 In the experiment, three sugar cubes were arranged closely together with 12 mm sides to form a shape measuring 19×36×20 mm. 3 The block is used as a template. Because the pores in the sugar cube are small, the mixture of PU and luminescent particles cannot easily enter it. Vacuum pumping can be used to create a significant pressure difference between the inside and outside of the sugar cube, which can accelerate the flow of the mixture and ensure the uniformity of the composite elastomer on the inside and outside of the sugar cube during curing.

[0107] The prepared composite luminescent elastomer porous structure is as follows Figure 7 The schematic diagram of the porous structure in (a) shows the distribution of internal pores and luminescent particles as follows. Figure 7 As shown in (b), (b) is a SEM image of the porous composite luminescent elastomer. The inset on the right is a magnified SEM image of a local area. It can be seen that the pore distribution is relatively uniform. However, due to the influence of particle settling under gravity during the curing process, the luminescent particles tend to concentrate on the pore surface on one side.

[0108] A three-dimensional X-ray microscope (Xradia 620 Versa, ZEISS) was used to image and observe the three-dimensional bulk distribution of a porous structure and luminescent particles (scanning imaging range: a cylinder with a diameter of 5.4 mm and a height of 7 mm). The results are as follows: Figure 8As shown, (a) is a three-dimensional perspective view of the porous structure combined with luminescent particles; (b) is a three-dimensional perspective view of only the luminescent particles; (c)-(e) are the front view, side view, and top view of the porous structure combined with luminescent particles, and the dimensions in the three figures are consistent. It can be seen that the overall distribution of luminescent particles in the three-dimensional bulk phase of the porous composite elastomer is relatively uniform. This indicates that, except for the concentration of luminescent particles on the pore surface caused by gravitational sedimentation, the introduction of the porous structure does not affect the uniform dispersion of luminescent particles in the entire three-dimensional bulk phase of the flexible matrix.

[0109] To visually compare the luminescent effects of dense and porous composite elastomers, during the fabrication of the porous structure, an additional mixture of PU and luminescent particles was added to the mold. The excess mixture was then allowed to solidify above the porous portion, forming a dense composite luminescent elastomer (approximately 10 mm thick). Figure 9 As shown in (a), Figure 9 (b) The luminescence effect of compressed porous and dense composite elastomers under indoor lighting conditions; Figure 9 (c) The luminescence effect of the porous and dense composite elastomer under compression in a darkroom. Compression of the upper and lower surfaces of the sample ensures that the load states of the porous and dense portions are essentially the same. The luminescence process of the composite elastomer was recorded by pressing the dense and porous composite elastomer under pressure using a commercial camera (EOS R6 Mark II, Canon). The luminescence of the dense portion of the composite elastomer is difficult to observe in both indoor lighting and darkroom conditions, while the luminescence of the porous portion is visible to the naked eye under indoor lighting. The difference is even more significant in the darkroom. This demonstrates that the porous structure significantly enhances the mechanoluminescence intensity and strengthens the luminescence response in the compression direction.

[0110] Further quantitative measurements of the spectrum and light intensity of the compression composite elastomer were performed using a measuring device consisting of a general-purpose mechanical testing instrument (UMT-5, Bruker) and an optical measurement system, such as... Figure 10 As shown in (a). The optical measurement system is consistent with the spectrometer and single-photon counter used when testing the samples of Example 1 and Comparative Example 1. The spectrum and intensity of the light emitted by the composite elastomer under different pressures are measured through an optical fiber. With the compression and recovery velocity maintained at 23.7 mm / s, the light intensity results of the composite elastomer when the applied pressure is at its maximum of 10 kPa, 50 kPa, and 100 kPa are as follows. Figure 10 As shown in (b), compared to the dense portion, the light intensity of the porous composite elastomer increased by 3098%, 842%, and 787% with increasing pressure load, respectively. The light intensity measurement results quantitatively demonstrate the significant enhancing effect of the porous structure on the mechanoluminescence of the composite elastomer in the compression direction.

[0111] Simultaneously, the mechanical property parameters of the composite elastomer and the pure PU elastomer were measured using UMT during compression, and their compression stress-strain curves are shown below. Figure 10 As shown in (c). Compared to pure PU elastomer, the addition of luminescent particles significantly enhances the compressive modulus of the dense ZnS:Cu / PU elastomer. The introduction of the porous structure greatly reduces the compressive elastic modulus of the composite elastomer. Under the premise that the flexible matrix and the luminescent particles have a high bonding force, this greatly improves the compressive deformation capacity of the composite elastomer, which is conducive to increasing the deformation of the elastomer under the same load, and thus improving the luminescence intensity during the compression deformation process.

[0112] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0113] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for preparing a mechanoluminescent elastic composite material, characterized in that, The steps include the following: The raw materials of the mechanoluminescent elastic composite material are mixed and then subjected to a first curing process to obtain the mechanoluminescent elastic composite material. The raw materials of the mechanoluminescent elastic composite material include a flexible matrix precursor and luminescent particles. The flexible matrix precursor is cured to form the flexible matrix of the mechanoluminescent elastic composite material. The flexible matrix precursor and the luminescent particles are mixed evenly according to the ratio of the flexible matrix precursor and the luminescent particles in the raw material and poured into the cavity of the hollow mold. After degassing for 10 minutes under a vacuum of -0.09MPa, a second curing is carried out to form a composite material test sample. The tensile elastic modulus of the composite material test sample is A. The flexible matrix precursor is cast into the cavity of a hollow mold, degassed for 10 minutes under a vacuum of -0.09 MPa, and then subjected to a third curing process to form a flexible matrix test sample. The tensile elastic modulus of the flexible matrix test sample is B. The conditions for the second and third curing processes are exactly the same as those for the first curing process; A and B satisfy: (AB) / B≥25%; The difference between the Zeta potential of the flexible substrate test sample and the Zeta potential of the luminescent particles is ≥10mV.

2. The method for preparing the mechanoluminescent elastic composite material according to claim 1, characterized in that, It meets at least one of the following characteristics: (1) The raw materials of the mechanoluminescent elastic composite material satisfy the following: 25% ≤ (AB) / B ≤ 100%; (2) The raw materials of the mechanoluminescent elastic composite material satisfy the following: the difference between the Zeta potential of the flexible matrix test sample and the Zeta potential of the luminescent particles is ≥15mV.

3. The method for preparing the mechanoluminescent elastic composite material according to claim 1, characterized in that, It meets at least one of the following characteristics: (1) The material of the luminescent particles includes any one or more of zinc sulfide doped with copper, zinc sulfide doped with manganese, strontium sulfide doped with copper, and strontium sulfide doped with cerium; (2) The luminescent particles have an aluminum oxide coating layer, the thickness of which is 10 nm ~ 2 μm; (3) The D50 particle size of the luminescent particles is 20 μm - 30 μm.

4. The method for preparing the mechanoluminescent elastic composite material according to claim 1, characterized in that, It meets at least one of the following characteristics: (1) The flexible matrix precursor includes any one or more of polyurethane prepolymer, modified polydimethylsiloxane prepolymer, and modified polyethylene terephthalate prepolymer; (2) The visible light transmittance of the flexible substrate is ≥85%.

5. The method for preparing the mechanoluminescent elastic composite material according to claim 1, characterized in that, In the raw materials of the mechanoluminescent elastic composite material, the mass percentage of the luminescent particles is 20% to 40%.

6. The method for preparing the mechanoluminescent elastic composite material according to claim 5, characterized in that, The luminescent particles are zinc sulfide-doped copper coated with alumina.

7. The method for preparing the mechanoluminescent elastic composite material according to claim 6, characterized in that, The flexible matrix precursor is a polyurethane prepolymer.

8. The method for preparing the mechanoluminescent elastic composite material according to claim 7, characterized in that, The polyurethane prepolymer includes at least one of the following characteristics: (1) The polymer monomers of the polyurethane prepolymer include polytetrahydrofuran and toluene-2,4-diisocyanate. Optionally, the molar ratio of polytetrahydrofuran to toluene-2,4-diisocyanate is 1:2 to 1:2.

2. (2) The chain extender of the polyurethane prepolymer is any one or more of N-methyldiethanolamine, diethanolamine, triethanolamine, 1,4-butanediol, and methylpropanediol; (3) The number average molecular weight of the polyurethane prepolymer is 40,000 g / mol to 70,000 g / mol.

9. The method for preparing the mechanoluminescent elastic composite material according to claim 1 or 2, characterized in that, The first curing step after mixing the raw materials of the mechanoluminescent elastic composite material includes: The raw material of the mechanoluminescent elastic composite material is introduced into a mold for first curing, and the cured material is separated from the mold; the mold is a hollow mold or a mold with pores; optionally, the mold with pores can be dissolved in a solution to achieve separation from the cured material.

10. A mechanoluminescent elastic composite material, characterized in that, It includes a flexible matrix and luminescent particles distributed in the flexible matrix, and is prepared by the method for preparing the mechanoluminescent elastic composite material according to any one of claims 1 to 9.

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